Electric resistance water heater



Aug. 22, 1950 D. B. MINER ELECTRIC RESISTANCE WATER HEATER Filed July l0, 1947 Patented Aug. 22, 1950 UNITED STATES *PATENT OFFICE 1.0 Claims.

This invention 4relates to domestic electric water heaters -of the resistance type, for use with upright .boilers or storage tanks.

An object of the invention is to provide an improved resistance .type water heater for use in connection with domestic water boilers or tanks, the said heater being characterized by extremely high efficiency and low cost.

A further object -of :the -invention is to provide an improved electric Water yheater as above which is soorganized as to result in the depositing of a minimum of scale and other solids on the heater walls whereby reliable and trouble-free ope-ration is had over an extended period of use.

Still .another `object `of the invention is to .provide an electric heater as characterized above, having an improved mounting for an automatic control whereby -the control is readily and quickly .removable and replaceable without disturbing the hydraulic system of .the heater or boiler.

A still .further object of the invention is to provide an improved automatically .controlled resistance .type .electric water .heater vfor use with upright Vboilers or tanks, wherein a relatively large supply of .hot water .is produced during the 1 5' its ends with an upright storage tankor boiler to f carry 'circulating .water passing from .and to .the tank. The metal tube Sis preferably although not necessarily loilarger .diameter .than the diameter of the pipes between fit .and the connecting tank.

On the outside of the tube and electrically .in- .i

sulated from Vit but in intimate heat relation therewith, a novel 'heating coil is provided, consisting of Acommercial grade copper wire, preierably enamel covered. vrlhe .copper wire is wound on the tube in vspaced convolutions, and

considering the rated current or power consumption of the heater, covers a relatively .large area `of the tube .as compared with 'the area which would be covered for va similar power consumption if wire of high resistance alloy were used `for the coil.

An elicient heat-exchange is provided between the copper coilandcopper tube by irst wrapping 'the tube with lapped turns of bre glass fabric tape, over which the copper wire is wound. After the winding of the copper coil it is coated with a heat resistant impregnating substance .such as a silicone varnish, the said varnish serving to anchor the convolutions of the ,coil and maintain the spacing of the said convolutions, and the varnish impregnating he glass tape .insulation and providing a unitary overall assembly of tube, insulation and .heating coil, the parts of which yare securely maintained in their original predetermined relationship. The fibre glass tape 4and silicone varnish '.efliciently Aelectrically insulate the coil from the tube, and also insulate the individual convolutionsof the coil iromveach other.

By this organization I have found that i-rst,

l an extremely efhcient and eective heat `ex change is provided between the copper tube and copper coil; second, .that heating .and cooling .of the assembly does not disturb .or dislocate .the components thereof due to differences in thermal expansion which exist .between .the @Opper and insulating material; and third, that for a given wattage input .a relatively large heat-.exchange area of Icoil and tube .is had. This latter enables a given volume .of water to be quickly and eiiciently heated by the present improved heater w'hilea-t the same time relatively low .temperatures may exist in the walls of .the tube as compared with temperatures encountered in resistance heaters wherein alloy resistance wire is utilized. In consequence yof this .improved organization and low-.temperature heating, ,boiling, bubbling or distillation at .the .walls of the heating tube is maintained at an .extremely low value or may be non-existant, and therefore, .the deposition of scale, minerals and .other solid substances on the walls of the tube is largely obviated. By this organization, therefore, the heater maintains .a high degree o efficiency .and does not clog up in use, especially where hard water is being heated, and a uniform and -reliable operation is had at all times, over an extended anol long period yor use.

By the provision of the efiicient :heat exchanging structure above mentioned, the copper wire resistance coil may `be .made to carry a current greatly in excess of the ratinU normally iconsidered safe, without danger vof the wire becoming over-heated and burningout, solong as .water is present in the `tube of the heater. Moreover, by the construction wherein the heat per unit area is maintained at a relatively low value, .the likelihood of steam being formed by the `heater to cause to the. system, should the heater be .inadvertently allowed to .remain on continuously, is obviated.

In the upper portion of the tube on which the copper heating coil is wound a transverse well is provided, extending into the tube and being permanently sealed thereto so that water cannot escape. The walls of the well are subjected to the heated water which is leaving the top of the tube, and a thermostatic element operatively connected with a circuit-controlling switch for the heating coil is inserted in the well so as to be subjected to the heat of the heated water. The control comprising the thermostatic element and switch means thereof is frictionally held in place by a simple spring clip, and therefore after disconnection of the wires to the switch, the control may be easily and conveniently removed without disturbing the hydraulic system of the heater, or of the tank connected with the heater. Therefore servicing and/or replacement of the control is reduced to a simple operation which may be done quickly and economically.

In one form of the invention illustrated herein a second tube is disposed within the tube on which the coil is wound, so as to be substantially vcoextensive therewith, and both ends of the second tube are open. At its top the second tube admits the well in which the thermostat control is carried, and I have found that by this organization a greater volume of hot water may be produced during the initial stage of heating of the coil, due to the effect being had of a delayed action of the thermostat. This is acornplished by the cold water which enters the lower ends of the tubes and travels upward in the inner tube, this water remaining relatively cool since it is heated much less than the water in the outer tube. In consequence of this, the average heat to which the thermostat is subjected is less than that which it would experience without the provision of the inner tube. Therefore the thermostat is not caused to operate as soon, and a greater quantity of water will thus be heated during the initial heating interval of the thermostat than would be heated without the use of the inner tube, since the initial heating interval is longer. Also, this is accomplished without raising the temperature setting at which the thermostatic switch will be opened, and there- Vfore the safety factor provided by the thermostat is'not altered since it will still respond to the same predetermined temperature as when the inner tube is not employed.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Figure l is an elevational view of the improved heater of this invention, connected with a hot water tank to carry circulating water passing VtoA and from the tank.

:ing period of the heater, and

Fig. 6 is a transverse sectional view of a water 'heating tube and a heating coil illustrating anothermodication of the invention.

Referringto Figs. l and 2, the improved electric water heater of this invention comprises a metal tube IIJ which is of non-magnetic metal, preferably copper, the ends of the tube being permanently secured, as by silver soldering, to iianges II of reducing ttings I2 which receive pipes I3 and I4 connected respectively to the lower and upper portions of an upright water tank I5. The tube I0 is thus connected to carry circulating water which passes to and from the tank I5.

According to the invention, the tube It is wrapped with electrical insulation which is resistant to high temperatures and at the same time has high thermal conductivity, the said wrapping comprising fabric tape It formed of glass bres and wrapped around the tube IE) in overlapping convolutions. Over the wrapped tape IG a heating coil I'I of copper wire I8 is wound, the said wire being preferably enamel covered and wound in spaced convolutions, and having a relatively great length in View of the wattage of the heater, so as to cover a relatively large area on the outside of the tube I9. The c oil II of wire I8, whether bare or enamel covered, is coated with a heat resistant electrically insulating varnish having high heat conductivity, such as a silicone varnish, the said coating being shown at I9 Fig. 3, and serving to anchor the wire I8 to the tape wrapping I6. The silicone varnish also impregnates the tape IS andy adheres the latter to the copper tube IB whereby theV tube, tape and coil are formed into a unitary assemblage. Y

It will be noted that the copper wire I8 is unsheathed, that is, devoid of any covering of substantial thickness which might appreciably interfere with the transfer of heat from the wire to the tube I0. It is intended that the word unsheathed as used hereinafter be construed as defining either a bare wire, or an enameled wire having a coating not exceeding one or two thousandths of an inch, such as is found in commercial grade enameled wire.

Due to the low resistance of the copper wire I 8 forming the coil Il, it has a great length for a given wattage input, and therefore covers a relatively large area of the tube IB; as a consequence the input or heat per unit covered area of the tube I0 is relatively low, and the operating temperature of the tube is relatively low. Also, by

the provision of the glass fibre tape it and silicone varnish coating I9, an effective electrical insulation is provided between 'the coil Il and tube IB and at the same time an eflcient exchange of heat is had betweenthe coil and tube. As a result of this latter, the operating teinperature of the coil vI'I is not greatly different from the temperature of the tube I5, the said temperatures being largely controlled by the temperature of the water inside the tube.

Because of the relatively low operating temperature of the tube I0 for a given adequate wattage rating of the heater, a satisfactorily large volume of water may be heated in a given time with a minimum of bubbling of the water, or distillation of solids from the water and depositing of same on the inner walls of the tube I Therefore, especially where the heater is used in conjunction with hard water, the tendency for scales or deposits to be formed on the inner walls 0f the tube I!) is held to a minimum, resulting inY an efficient and reliable heating of v,water being had over a longand extended pe- 5. sothat overheating of the coil is prevented at all times that water is present. Due to the high heat conductivity of the copper of the tube I0 and of the coil l'l and the efficient heat exchange between these, the coil l'l may carry a current greatly in excess of that normally considered safe for copper wire oi the size used, without resulting in the wire IS becoming excessively hot or approaching burnout temperatures. This is true so long as any water exists within the tube Iii.

I have found that by this organization, over an extended period of use of the heater, water may be heated more effectively and quickly than when high resistance alloy is used as the resistance wire, due to the lower operating temperature of the coil l? and tube l, and the substantially larger area of the tube itl which is covered by the coil i i and heated thereby and which area is as a consequencel transmitting heat t0 the water in the tube.

Where nickel alloy (Nichrome) or other high resistance alloys haver been used in the past in a heating coil the area covered by the Nichrome coli and which transmits heat to the part carrying the circulating water is considerably less than that provided in the present improved heater, and as a consequence operating temperatures are much higher, resulting in boiling, bubbling anddistillation of the water inside of the heating tube. If for the same wattage heater it were attempted to use Nichrome or other similar alloy to cover the same area of tube covered by the novel copper wire heating coil of the present invention, then the crosssectional area of the Nichrome wire would have to be excessively great to provide the proper wattage, and unless special rectangular shapes were resorted to, a multi-layer coil would have to be employed. This would result in increased fabrication costs, and greatly increased wire costs, and a reduction in the efiiciency of heatexchange between the coil and tube.

Where Nichrorne wire is used to cover a smaller tube area, in spite oi the shorter length of Nichi-orne, the cost of the Nichrome wire is greatly in excess of the cost of the greater length of copper wire used herein, in addition to the undesirable eiiect being had of bubbling, distillation of water, etc. Depositing of solids thus occurs, and is quite marked where hard Water .is-used, and eventually these solids cause a coating or scale on the inside of the heating tube, resulting in a marked reduction of transfer of to the water and in general impairing and adversely alecting the efliciency of the heater. Also, such deposits cause the operating temperature of the alloy resistance wire to become higher than that for which the unit is designed, resulting in dangerous temperatures being approached and eventually causing burnout of the resistance coil. Moreover, such higher temperatures are wasteful since for a given thickness of heat insulation they cause more heat to be lost externally of the heater, which heat serves no useful purpose. According to the present inven-v tion, however, whereby it is possible to raise the desired quantity of water to the desired temperature by use of lower operating temperatures in the heater, less heat is lost externally of the heater and therefore less heat is wasted or dissipated without serving a useful purpose.

Referring to Fig. 2, the tube Il] and heating coil il are wrapped with a thick layer of heat insulation 2@ which is enclosed in a metal jacket 6 2l secured in place by end plates 22 engaging the reducing fittings l2.

In accordance with the invention, for the purpose of effectively controlling the temperature of the heating coil Il and of the water heated thereby, and to enable quick and convenient servicing of such control, the upper portion of the tube I` is provided with a transversely extending well in the form of an open-ended tube 23 which passes through the walls of the tube IU and is silver soldered or otherwise sealed thereto so as to prevent leakage of water therefrom. The tube 23 is of course much smaller in diameter than the tube i El so that water may circulate through the latter tube upwardly past the tube or well 23.

In the well 23 a thermostat element 24 is located, connected to a switch housing 25 in which a circuit controlling switch 26 is carried for actuation by the element 24. The switch 26 is connected to control the heating coil Il, and connection is made to an exterior current supply through a ilexible conduit 21 which is secured to the switch housing 25.

The thermostat element 24, adjacent the housing has an enlarged detent collar 28 having recesses or depressions is engageable by spring ngers secured to the tube 23 whereby the element 526i and housing 25 are frictionally retained in place and may be removed when desired merely applying a pulling force thereto. By this construction., removal of the thermostat 2d and housing 25 does not involve the hydraulic circuit of the heater at all, and may therefore be done in a simple manner and without loss of time tor servicing operations if this should be necessary.

Referring to 4 each end of the wire l 8 constituting the heating coil il may be wrapped around the eye of a connector lug 3i and soldered thereto, the said lug being electrically connected with lead wires 32 as shown.. The lug 3i is disposed to lie fia-t against the fibre glass tape it so that the end portions of the wire iS are in intimate contact with the tape, thereby preventing overheating ci said ends by virtue of the heat transfer to the tube i9 being maintained.

A. modication of the invention is shown in Fig. 5, wherein means are provided for causing a delayed action of the thermostat 25;' during the initial heating period of the heater. This means comprises a metal tube 33 mounted within the tube lil and substantially coextensive therewith, both ends of the tube S3 being open and the lower end being supported in the tube l by means 0I" struts 35. rhe upper end of the tube 33 receives and is supported by one end oi a tube 23a constituting a well for the thermostat 24, the inner end of the tube 23a being closed as shown. rShe remainder of the heater shown in Fig. 5 is substantially the same as the heater of Figs. l through e, and like parts have been given like characters.

lThe operation of the heater of Fig. 5 is as iollows: Circulating water entering the lower end of the heater travels upward through the tube i5) and also through the tube 33. This entering water is cold or cool, and as-it travels upward in the tube Iii it is heated by the heating coil ll. The water ascending in the tube 33 is not heated as rapidly as the water in the tube l@ and therefore has a lower temperature, and this water of lower temperature comes into contact with the inner end of the well 23a and causes the average tempenature of the said well to be less than the temperature vof the Well `23 in Figs. l through 3.. As a consequence, during the initial heating of the heater the thermostat .24 will not be operated to open the circuit of the .heating coil :l1 as soon as it will inthe heater without the inner tube 33. In other words, more heat will be imparted to the water in the tank i5 before the thermostat 24 operates to initially open the vcircuit of the -coil l1, and therefore more hot water .will be available for use after initial turning on of the heater. All this is accomplished without raising the cut-eli temperature of the thermostat 24, and therefore the safety factor afforded by the thermostat is not adversely eiected even though in eiect its action is delayed.

Preferably the tube 23a is silver soldered to both the outer tube lil `and the inner tube 33 thereby to provide a Vmetallic connection whereby heat-exchange by conduction may take place between the tubes it, 23a and 33, resulting in more `unifornfiity in the temperature of the tube 23a, and thermostat Yelement 24.

Referring to Vthe 4modication of the .invention shown in Fig. 6, the fibre glass insulation between the copper wire heating coil Il and the tube l@ .is in the form of a single large sheet of iibre glass fabric, the said. sheet being wrapped around the tube and the edges lapped to provide a longitudinally extending lapped seam. Preferably, the iibre glass fabric is impregnated with a heat ret sistant silicone varnish, and is calendered to provide a very smooth surface on both sides. By this organization the application of the insulation to the tube i6 is simplified, and a more uniform condition of heat exchange is provided between the coil Il and the tube I0 due to the elimination of surface irregularities in the ilbre lglass insulation. To further improve the heatexchange between the coil Il and tube I9 the latter may be coated with silicone varnish prior to application of the fibre glass sheet, and this also simpliiies the assembly of the heater since the iibre glass sheet may be adhered to the `tube by such coating.

By the provision of the copper wire heating element il, an advantageous self-regulating effect is had by virtue of the high temperature coeiioient of resistance of the lcopper wire, .and therefore there is less likelihood of `dangerous overheating in the event of malfunctioning of the thermostat. Also, a quicker heating is obtained during the initial `period when `the heater is first turned on. For example, when the wire i3 of the heating coil H is cold, it has Va relatively low resistance, and therefore a. higher current lwill pass through it, causing it to heat relatively quickly. As the temperature oi the heating coil Il rises, the overall .resistanceof the coil will increase substantially due to the high temperature coeicient of resistance of copper. As a consequence of this latter, the operating current in the coil is reduced in proportion to the rise in temperature, and if the temperature should rise over the normal operating temperature of the unit, due to failure of the thermostat, the reduction of current in the coil il will 'become substantial eand tend to act as a safety lfeature. Thus, a self-regulating edect is had which is not present in heating elements using high resistance alloys.

By virtue of both the coil il and tube it* being made of copper, the thermal expansion of these willV be substantially equal, thereby resulting in a desirable mechanical stability of the .heating unit 8 comprising the'coil, tube and libre glass .insula tion thereof.

Variations and modifications may be made lwithin the scope of this invention and portions or the improvements may be used without others.

l claim:

l. An electric water heater for use with a stor age tank, ycomprising a metal tube having connections at its ends with the vsaid tank to carry circulating water .from :and to the tank, an electrical coil for heating the tube; a thermostatic control for .said coil, said control having an elongate vportion to `receive heat from the heated water; and a well for `carrying the elongate portion o'f the control, said well extending transversely into the tube adjacent one end thereof whereby water flows around the well in .directions substantially at righ-t angles to the well axis and said well being metallically sealed .to the tube and arranged to prevent water in the tube from e11- tering the well, the elongate portion of the control being removable rom the well without vdisturbing the said seal .and arrangement.

2. An electric water heater 'for use with a `storage tank, comprising a Ametal tube having connesn tions at its `ends with `the said tank to carry circulating water from and to the tan-k; an electrical coil lor heating the tube; a thermostatic control for said coil, said control having an elongate portion to receive heat from the heated water; and an open-ended tube for carrying the elongate porti-oh oi the control, said. tube extending transversely into and through the water tube whereby .water flows around the vopen-ended 'tube .in directions substantially at right 4aiu-gies to `the axis thereof .and said open-ended tube being sealed adjacent its ends Lto opposite walls of the water tube, said elongate :portion of the control being reinen/able from the transverse tube without disturbing the said seals.

1S. A water .heater for use with a storage tank., comprising a pair of elongate tubes located one within the other and extending substantially coextensive with each other, the inner tube being open at both ends Aand the outer tube being adapted for Aconnection Aadjacent its ends With said tank to enable the tubes to carry circulating water passing from and `to the tank; means for heating the walls of the outer tube; and a thermostatic control for said heating means, said control being arranged .in heat-exchanging relation with water in both the inner and outer tubes whereby the `action ofthe Acontrol is delayed during initial operation of the heater, .said heater being operable with the tubes thereod in a substantially vertical position.

al A Water heater :for use with a storage tank, comprising a pair .of elongate tubes located 4one within the other and extending substantially coextensive with each other, lthe inner tube being open at both ends yand the outer tube being adaptior connection Aadjacent its ends with said tank to enable the tubes to carry circulating water passing vfrom and to the tan-k; means for heating the walls-of the outer tube; and `a thermostatic control for said heating means, said control being arranged in heat-exchanging relation with water in both the inner and outer tubes whereby theaction of the control is delayed during initial operation of the heater, said heater being operable with the tubes thereof in a substantially vertical position and the thermostatic control being located adjacent the upper ends of the tubes.

5. A Water heater for use with a storage tank,

comprising a pair of elongate tubes located one Within the other and extending substantially coextensive with each other, the inner tube being open at both ends and the outer tube being adapted for connection adjacent its ends with said tank to enable the tubes to carry circulating Water passing from and to the tank; means for heating the walls of the outer tube; and a thermostatic control for said heating means having an elongate portion for exposure to heat; and a well for carrying said elongate portion, said well extending transversely into the inner and outer tubes whereby the action of the control is delayed during initial operation of the heater, said heater being operable with the tubes thereof in a substantially vertical position, and said well being sealed to the outer tube and arranged to prevent water in the tubes from entering the Well, the elongate portion of the control being removable from the well without disturbing the said seal and arrangement.

6. A Water heater for use with a storage tank, comprising a pair of elongate tubes located one Within the other and extending substantially coextensive with each other, the inner tube being open at both ends and the outer tube being adapted for connection adjacent its ends with said tank to enable the tubes to carry circulating water passing from and to the tank; means for heating the walls of the outer tube; and a thermostatic control for said heating means having an elongate lportion for exposure to heat; and a closed-end tube for carrying said elongate portion, said tube extending transversely into the inner and outer tubes whereby the action of the y.control is delayed during initial operation of the heater. said heater being operable with the tubes thereof in a substantially vertical position, and said closed-end tube being sealed to the said outer tube and arranged with its open end out to prevent Water in the inner and outer tubes from entering the closed-end tube. the elongate portion of the control being removable from the closed-end. tube without disturbing the said seal.

7. A Water heater for use with a storage tank, comprising a pair of elongate tubes located one within the other and extending substantially coextensive with each other, the inner tube being onen at both ends and the outer tube being adapted for connection adiacent its ends with said tank to enable the tubes to carry circulating water passing from and to the tank; metal means for heating the Walls of the outer tube; and a thermostatic control for said heating means, having an elongate portion for exposure to heat; and a well for carryingr said elongate portion. said well extending transverselv into the inner and outer tubes whereby the action of the control is delayed during initial operation of the heater, said heater being operable with the tubes thereof in a substantially vertical position, and said well being metallically sealed and ioined to the inner and outer tubes to provide for conductive heat exchange between the well and said tubes.

8. A water heater for use with a storage tank, comprising a pair of elongate tubes located one Within the other and extending substantially coextensive with each other, the inner tube being open at both ends and the outer tube being adapted for connection adjacent its ends with said tank to enable the tubes to carry circulating Water passing from and to the tank; means for heating the Water in contact with the inner Wall of one tube substantially at the said contact; and a thermostatic control for said heating means, said control being arranged in heat-exchanging relation with Water in both the inner and outer tubes whereby the action of the control is delayed during initial operation of the heater, said heater being operable With the tubes thereof in a substantially vertical position.

9. A water heater for use with a storage tank, comprising a pair of elongate tubes located one Within the other and extending substantially coextensive with each other, the inner tube being open at both ends and the outer tube being adapted for connection adjacent its ends with said tank to enable the tubes to carry circulating Water passing from and to the tank; means for heating the Water in contact with the inner wall of one tube substantially at the said contact; and a thermostatic control for said heating means, having an elongate portion for exposure to heat; and a well for carrying said elongate portion, said Well extending transversely into the inner and outer tubes whereby the action of the control is delayed during initial operation of the heater, said heater being operable with the tubes thereof in a substantially vertical position, and said well being sealed to the outer tube and arranged to prevent Water in the tubes from entering the well, the elongate portion of the control being removable from the Well Without disturbing the said seal and arrangement.

l0. A water heater for use with a, storage tank, comprising a pair of elongate tubes located one within the other and extending substantially c0- extensive with each other, the inner tube being open at both ends and the outer tube being adapted for connection adjacent its ends with said tank to enable the tubes to carry circulating Water passing from and to the tank; means for heating the Water in contact with the inner Wall of one tube substantially at the said contact; a thermostatic control for said heating means, having an elongate portion for exposure to heat; and a Well for carrying said elongate portion, said Well extending transversely into the inner and outer tubes whereby the action of the control is delayed during initial operation of the heater, said heater being operable with the tubes thereof in a substantially vertical position, and said well impeding water flow through the tube at whose Wall the water is heated, to a relatively less extent than it impedes water flow through the other tube.

DONALD B. MINER.

REFERENCES CITED The following references are of record in the 

